ECG was first used in the beginning of the twentieth century. Over the last several decades, a variety of diagnostic procedures have been developed for sensing and analyzing activity of the human heart. These include electrocardiography, vectorcardiography and polarcardiography, all of which depend upon related instrumentation used to produce records derived from voltages produced by the heart on the surface of the human body.
The records so produced are graphical in character and require interpretation and analysis to relate the resulting information to the heart condition of the patient or other subject. Historically, such records have been produced directly as visible graphic recordings from wired connections extending from the subject to the recording device. With advances in computer technology, it has become possible to produce such records in the form of digitally stored information for later replication or retrieval and analysis. Likewise, with advances in communication technology, remote or wireless sensing has become possible.
The production of a conventional 12 lead electrocardiogram (also sometimes referred to as an ECG) involves the placement of 10 lead electrodes (one of which is a ground or reference electrode) at selected points on the surface of a subject's body. Each electrode acts in combination with one or more other electrodes to detect voltages produced by depolarization and repolarization of individual heart muscle cells. The detected voltages are combined and processed to produce 12 tracings or “leads” of time varying voltages. The leads so produced are as follows:
LeadVoltageIvL − vRIIvF − vRIIIvF − vLaVRvR − (vL + vF)/2aVLvL − (vR + vF)/2aVFvF − (vL + vR)/2V1v1 − (vR + vL + vF)/3V2v2 − (vR + vL + vF)/3V3v3 − (vR + vL + vF)/3V4v4 − (vR + vL + vF)/3V5v5 − (vR + vL + vF)/3V6v6 − (vR + vL + vF)/3
In this standard, which is the most widely used system for making short term electrocardiographic recordings of supine subjects, the potentials indicated above, and their associated electrode positions, are as follows:
vL potential of an electrode on the left arm;
vR potential of an electrode on the right arm;
vF potential of an electrode on the left leg;
v1 potential of an electrode on the front chest, right of sternum in the 4th rib interspace;
v2 potential of an electrode on the front chest, left of sternum in the 4th rib interspace;
v4 potential of an electrode at the left mid-clavicular line in the 5th rib interspace;
v3 potential of an electrode midway between the v2 and v4 electrodes;
v6 potential of an electrode at the left mid-axillary line in the 5th rib interspace;
v5 potential of an electrode midway between the v4 and v6 electrodes; and
vG (not indicated above) is a ground or reference potential with respect to which potentials vL, vR, vF, and v1 through v6 are measured. Typically, though not necessarily, the ground or reference electrode is positioned on the right leg. As is apparent from the foregoing, a 12 lead system uses 10 electrodes on a patient's body.
Six lead electrocardiograms are also known. These systems do not use any chest electrodes and so, only utilize electrodes placed on the left and right arms, and left and right legs. Accordingly, these systems use a total of 4 electrodes on a patient's body.
Correct interpretation of an ECG requires a great deal of experience since it involves familiarity with a wide range of patterns in the various leads. Any ECG which uses an unconventional system of leads necessarily detracts from the body of experience that has been developed in the interpretations of conventional ECGs, and may therefore be considered generally undesirable. The leads generated would be understandable only by a relative few who were familiar with the unconventional system. Despite its widespread use, clinicians acknowledge that modern ECG analysis suffers from insufficient sensitivity and specificity.
Because of the disadvantages of regular ECG methods and despite a common opinion that all fruitful information from ECG has already been determined by analysis of standard PQRST wave properties, the present inventors developed a method which surpasses regular ECG analysis. That development is the subject U.S. Pat. No. 6,694,178, herein incorporated by reference. A description of the PQRST complex is provided in the '178 patent. The '178 patent describes a method of conversion of one ECG lead to produce a three-dimensional artificial topological model. The topological information of this model enables the extraction of useful information from low amplitude fluctuations of the initial signal. This information is simply unavailable from traditional methods of ECG analysis, as these methods consider most fluctuations, as noise.
However, this method of ECG analysis according to the '178 patent has two principle limitations. First, not all pathological states of a heart appear in one lead. For example, small focal (transmural) myocardial infarctions are, in many instances, impossible to reveal from one lead. Secondly, using only one lead in a number of cases, causes various diseases having similar topological images, to be indiscernible from one another. Specifically, the information associated with one lead is insufficient for identifying excitation direction and sharing of changes on the left and right atriums, and left and right ventricles. Therefore, the method of the '178 patent is effective only for detection of certain deviations, but is ineffective for derivation of diseases, in which the exact definition of the type of deviation and its localization must be determined.
To overcome these disadvantages, the present inventors proceeded from the analysis of fluctuations of one lead, i.e. analysis of electrical potentials at one point on the surface of a patient's body, to analyze the fluctuations of electrical potentials at several surface points on a body. This strategy is the subject of DE 199 33 277 A1. This strategy enables the construction of a topological model with 12 standard ECG leads. The topological model of a heart in this strategy provides different color patterns for different diseases, and so, allows an effective diagnosis of disease type. However, the topological heart model of a patient constructed by this strategy has a strictly discrete structure because the field of electrical fluctuations on the surface of the patient's body is determined from only a relatively small number of surface points. As a result, surface points, which are not laying on lines of standard ECG leads, do not participate in forming the topological model. Therefore, when surface potentials are constant at the points (i.e. locations of the 10 electrodes) of the standard 12 lead system, but changes occur at other points, the topological model does not show these changes. Electrical fluctuations occurring at regions besides the locations of the electrodes in a 12 lead system can be very important for early detection of many pathologies. For example, there is a wide group of clinically important hidden cases of ischemic disease (a decrease in blood supply), which are not revealed by a standard 12 lead system of a resting ECG but which may be indicated by detection at other points. Therefore, the approach described in DE 199 33 277 A1 is unable, or at least severely deficient, in identifying such conditions, thus leading to unexpected clinical consequences.
The present discovery described herein provides a dramatic improvement in ECG analysis in comparison to currently known ECG analysis available today.